Interpretive Summary: Dissolved organic matter (DOM) derived from fresh organic materials such as leaves and manure may play an important role in the process of organic matter accumulation in soils. In this study, eight DOM samples from alfalfa, corn, crimson clover, hairy vetch, lupin, soybean, wheat and dairy manure were investigated with several advanced techniques for a better understanding of how DOM composition might influence soil organic matter properties. All DOM sources were primarily composed of soluble carbohydrates, as well as some other soluble organic compounds such as organic acids, amino acids, and phenolic compounds. In contrast, dairy manure displayed properties characteristic of more highly decomposed material. This research may help us understand the effects of DOM on soil nutrient availability to plants.

Technical Abstract:
Dissolved organic matter (DOM) derived from fresh or early-stage decomposing soil amendment materials may play an important role in the process of organic matter accumulation. In this study, eight DOM samples from alfalfa, corn, crimson clover, hairy vetch, lupin, soybean, wheat and dairy manure were investigated using ultraviolet (UV)-visible, Fourier-transform infrared (FT-IR), solution P-31 and solid state C-13 nuclear magnetic resonance (NMR)spectroscopies. UV-visible and FT-IR spectra of the plant-derived DOM samples were typical for natural organic matter, but possessed less humic-like characteristics than dairy manure-derived DOM. The C-13 NMR spectra of the seven plant-derived DOM samples indicated that they all were primarily composed of sugars, amino acids or peptides and low-molecular carboxylic acids. Carbohydrates are dominant components with very few aromatics present. In addition, DOM from crimson clover and lupin, but not other three leguminous plant DOM samples, contained significant asparagine. On the other hand, DOM from corn and wheat contained less amino acids or peptides. The spectra of DOM of dairy manure revealed the presence of significant amounts of nonprotonated carbons and lignin residues, suggesting humification of the manure-derived DOM. Significant carbohydrates as well as aromatics were present. The P and C bonding information for these DOM samples may be useful for understanding the effects of DOM on soil nutrient availability to plants.